REVIEW: Hyperammonemia is a metabolic condition characterized by elevated levels of ammonia in the blood. Increased entry of ammonia to the brain is a primary cause of neurologic disorders, such as congenital deficiencies of urea cycle enzymes, hepatic encephalopathies, Reye syndrome, several other metabolic disorders, and some toxic encephalopathies. Signs and symptoms of early-onset hyperammonemia (neonates) may include the following: - Lethargy - Irritability - Poor feeding - Vomiting - Hyperventilation, grunting respiration - Seizures Signs and symptoms of late-onset hyperammonemia (later in life) may include the following: - Intermittent ataxia - Intellectual impairment - Failure to thrive - Gait abnormality - Behavior disturbances - Epilepsy - Recurrent Reye syndrome - Protein avoidance - Rarely, episodic headaches and cyclic vomiting Diagnosis No specific physical findings are associated with hyperammonemia. Affected infants usually present with the following: - Dehydration - Lethargy - Tachypnea - Hypotonia - Bulging fontanelle Examination occasionally reveals a peculiar finding, such as odor of sweaty feet in isovaleric acidemia or abnormally fragile hair in argininosuccinic aciduria. Infants with argininosuccinic lyase deficiency may present with hepatomegaly. Perform the following tests in patients with suspected hyperammonemia: - Arterial blood gas analysis - Serum amino acid levels - Urinary orotic acid levels - Urinary ketone tests - Plasma and urinary organic acid levels - Enzyme assays - DNA mutation analysis: Method of choice to confirm the diagnosis of urea cycle disorders - Heterozygote identification in ornithine transcarbamoylase deficient pedigrees The following imaging studies may be used in evaluating patients with hyperammonemia: - Neuroimaging: CT or MRI of the brain - MR spectroscopy Management The therapeutic aims in patients with hyperammonemia are to correct the biochemical abnormalities and ensure adequate nutritional intake. Treatment involves compounds that increase the removal of nitrogen waste. Pharmacotherapy Medications used in the treatment of hyperammonemia include the following: - Urea cycle disorder treatment agents (eg, sodium phenylbutyrate, carglumic acid, sodium phenylacetate, and sodium benzoate) - Antiemetic agents (eg, ondansetron, granisetron, palonosetron, dolasetron) Other treatments Other management approaches for hyperammonemia include the following: - Cessation of protein and/or nitrogen intake - Hemodialysis - Supportive care with parenteral intake of calories - Surgery Surgical intervention for patients with hyperammonemia include liver transplantation for correction of the metabolic error and/or liver cell transplantation as an alternative or bridge to liver transplantation
Posted on: Sat, 24 Jan 2015 12:52:19 +0000
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